BLKID(8) manual page
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blkid - locate/print block device attributes
blkid -L
label | -U uuid
blkid [-dghlv] [-c file] [-o format] [-s tag] [-t NAME=value]
[device ...]
blkid -p [-O offset] [-o format] [-S size] [-s tag] [-n list] [-u
list] device ...
blkid -i [-o format] [-s tag] device ...
The blkid
program is the command-line interface to working with the libblkid(3)
library.
It can determine the type of content (e.g. filesystem or swap) that a block
device holds, and also the attributes (tokens, NAME=value pairs) from the
content metadata (e.g. LABEL or UUID fields).
When device is specified, tokens
from only this device are displayed. It is possible to specify multiple
device arguments on the command line. If none is given, all devices which
appear in /proc/partitions are shown, if they are recognized.
Note that
blkid reads information directly from devices and for non-root users it
returns cached unverified information. It is better to use lsblk --fs to
get a user-friendly overview of filesystems and devices. lsblk(8)
is also
easy to use in scripts. blkid is mostly designed for system services and
to test libblkid functionality.
blkid has two main forms of operation: either
searching for a device with a specific NAME=value pair, or displaying NAME=value
pairs for one or more specified devices.
The size and offset arguments
may be followed by the multiplicative suffixes like KiB (=1024), MiB (=1024*1024),
and so on for GiB, TiB, PiB, EiB, ZiB and YiB (the "iB" is optional, e.g.
"K" has the same meaning as "KiB"), or the suffixes KB (=1000), MB (=1000*1000),
and so on for GB, TB, PB, EB, ZB and YB.
- -c cachefile
- Read from cachefile
instead of reading from the default cache file (see the CONFIGURATION FILE
section for more details). If you want to start with a clean cache (i.e.
don’t report devices previously scanned but not necessarily available at
this time), specify /dev/null.
- -d
- Don’t encode non-printing characters. The
non-printing characters are encoded by ^ and M- notation by default. Note
that the -o udev output format uses a different encoding which cannot be
disabled.
- -g
- Perform a garbage collection pass on the blkid cache to remove
devices which no longer exist.
- -h
- Display a usage message and exit.
- -i
- Display
information about I/O Limits (aka I/O topology). The ’export’ output format
is automatically enabled. This option can be used together with the -p option.
- -k
- List all known filesystems and RAIDs and exit.
- -l
- Look up only one device
that matches the search parameter specified with the -t option. If there
are multiple devices that match the specified search parameter, then the
device with the highest priority is returned, and/or the first device found
at a given priority. Device types in order of decreasing priority are:
Device Mapper, EVMS, LVM, MD, and finally regular block devices. If this
option is not specified, blkid will print all of the devices that match
the search parameter.
- -L label
- Look up the device that uses this filesystem
label; this is equal to -l -o device -t LABEL=label. This lookup method is
able to reliably use /dev/disk/by-label udev symlinks (dependent on a setting
in /etc/blkid.conf). Avoid using the symlinks directly; it is not reliable
to use the symlinks without verification. The -L option works on systems
with and without udev.
Unfortunately, the original blkid(8)
from e2fsprogs
uses the -L option as a synonym for -o list. For better portability, use
-l -o device -t LABEL=label and -o list in your scripts rather than the -L option.
- -n list
- Restrict the probing functions to the specified (comma-separated)
list of superblock types (names). The list items may be prefixed with "no"
to specify the types which should be ignored. For example:
blkid -p -n vfat,ext3,ext4
/dev/sda1
probes for vfat, ext3 and ext4 filesystems, and
blkid -p -n nominix /dev/sda1
probes for all supported formats except minix filesystems. This option
is only useful together with -p.
- -o format
- Use the specified output format.
Note that the order of variables and devices is not fixed. See also option
-s. The format parameter may be:
- full
- print all tags (the default)
- value
- print the value of the tags
- list
- print the devices in a user-friendly format;
this output format is unsupported for low-level probing (-p or -i).
This output
format is DEPRECATED in favour of the lsblk(8)
command.
- device
- print the
device name only; this output format is always enabled for the -L and -U
options
- udev
- print key="value" pairs for easy import into the udev environment;
the keys are prefixed by ID_FS_ or ID_PART_ prefixes
The udev output returns
the ID_FS_AMBIVALENT tag if more superblocks are detected, and ID_PART_ENTRY_*
tags are always returned for all partitions including empty partitions.
This output format is DEPRECATED.
- export
- print key=value pairs for easy
import into the environment; this output format is automatically enabled
when I/O Limits (-i option)
are requested
- -O offset
- Probe at the given offset
(only useful with -p). This option can be used together with the -i option.
- -p
- Switch to low-level superblock probing mode (bypassing the cache).
Note
that low-level probing also returns information about partition table type
(PTTYPE tag) and partitions (PART_ENTRY_* tags).
- -s tag
- For each (specified)
device, show only the tags that match tag. It is possible to specify multiple
-s options. If no tag is specified, then all tokens are shown for all (specified)
devices. In order to just refresh the cache without showing any tokens,
use -s none with no other options.
- -S size
- Override the size of device/file
(only useful with -p).
- -t NAME=value
- Search for block devices with tokens
named NAME that have the value value, and display any devices which are
found. Common values for NAME include TYPE, LABEL, and UUID. If there are
no devices specified on the command line, all block devices will be searched;
otherwise only the specified devices are searched.
- -u list
- Restrict the probing
functions to the specified (comma-separated) list of "usage" types. Supported
usage types are: filesystem, raid, crypto and other. The list items may
be prefixed with "no" to specify the usage types which should be ignored.
For example:
blkid -p -u filesystem,other /dev/sda1
probes for all filesystem and other (e.g. swap) formats, and
blkid -p -u
noraid /dev/sda1
probes for all supported formats except RAIDs. This option is only useful
together with -p.
- -U uuid
- Look up the device that uses this filesystem uuid.
For more details see the -L option.
- -V
- Display version number and exit.
If the specified token was found, or if any tags were shown from (specified)
devices, 0 is returned.
If the specified token was not found, or no (specified)
devices could be identified, an exit code of 2 is returned.
For usage or
other errors, an exit code of 4 is returned.
If an ambivalent low-level
probing result was detected, an exit code of 8 is returned.
The standard location of the /etc/blkid.conf config file can be overridden
by the environment variable BLKID_CONF. The following options control the
libblkid library:
- SEND_UEVENT=<yes|not>
- Sends uevent when /dev/disk/by-{label,uuid,partuuid,partlabel}/
symlink does not match with LABEL, UUID, PARTUUID or PARTLABEL on the device.
Default is "yes".
- CACHE_FILE=<path>
- Overrides the standard location of the
cache file. This setting can be overridden by the environment variable
BLKID_FILE. Default is /run/blkid/blkid.tab, or /etc/blkid.tab on systems
without a /run directory.
- EVALUATE=<methods>
- Defines LABEL and UUID evaluation
method(s). Currently, the libblkid library supports the "udev" and "scan"
methods. More than one method may be specified in a comma-separated list.
Default is "udev,scan". The "udev" method uses udev /dev/disk/by-* symlinks
and the "scan" method scans all block devices from the /proc/partitions
file.
blkid was written by Andreas Dilger for libblkid and improved
by Theodore Ts’o and Karel Zak.
- Setting LIBBLKID_DEBUG=0xffff
enables debug output.
libblkid(3)
, findfs(8)
, wipefs(8)
The
blkid command is part of the util-linux package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
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